Mobile work platforms typically include a cage or platform that is designed to receive one or more human operators. The cage is mounted on a lift mechanism, such as a hydraulic boom or a scissor lift mechanism, that allows its height to be adjusted. The mobile work platform also includes a wheeled or tracked chassis, which allows it to be moved easily to a desired location. Various types of mobile work platform are available, including self-propelled, self-drive, trailer and vehicle-mounted platforms.
A load monitoring system is generally included to provide cage overload protection. Cage overload protection is required on mobile elevating work platforms as defined by European standard EN280:2001 Amendment 1. European standard EN954 is cited by EN 280 and describes the requirements for safety switches in electrical systems providing overload protection. EN954 Category 3 requires that common mode faults resulting from damage to the protection system are taken into account, if the probability of such a fault occurring is significant.
One such fault may occur if the mechanical structure of the load protection system is damaged, causing the zero position of the load cell to shift in an unsafe direction. The resulting load measurement may then be inaccurate. There is currently no requirement for on-going calibration of load monitoring systems. It is thus possible for damage to the load monitoring system or the structure on which it is mounted to go undetected. This may allow the cage to be overloaded without triggering the protection system, causing the work platform to become unstable.
It is an object of the present invention to provide a mobile work platform and a load monitoring system for a mobile work platform that mitigate at least some of the aforesaid disadvantages. In particular, but not exclusively, the invention seeks to provide a detector within the load monitoring system for detecting any unsafe damage to the load monitoring system that may result in an unstable work platform.